Photographic overcoating



compositions.

United States Patent 3,105,762 PHOTUGRAPHIC OVERCOATING John F. Byrne and Philip F. Kurz, Columbus, Ohio, assignors, by mesne assignments, to Minneapolis-Honeywell Regulator Company, a corporation of Delaware No Drawing. Filed May 25, 1960, Ser. No. 31,555 4 Claims. (Cl. 9667) The present invention relates broadly tophotosensitive compositions and more particularly to photographic compositions of the print-out type. The invention relates specifically to an overcoating composition to be applied to such photosensitive base compositions which will improve the print-out characteristics of the photosensitive The term print-on refers to that type of photosensitive substance upon which a visible image is obtained after an exposure to light or other electromagnetic radiation has been initially utilized to form a latent image, the visible image being obtained simply by an additional exposure to such radiation, normally at a somewhat ilower intensity. This additional exposure is known as latensification and is general in its application, including exposing the area upon which the initial image was formed as Well as the surrounding background area to an added amount of radiation. The further discussion of the latensification type photographic compositions can be found in the application of Troy A. Scott, No. 737,758, filed May 26, 1958, and assigned to the same assignee as the present invention. 3

Photographic compositions of the print-out type showing the latensification have found use in oscillographic recording and the like. The invention, as disclosed in the Scott application noted above, is particularly adaptable to this type of recording in that it shows a sensitivity equivalent to 200,000 lineal inches per second capability. Utilizing the overcoating of the present invention, the over-all properties of the photosensitive material are enhanced and a decidedly superior product results.

We have found that the trace density and the stability of the trace of the invention of the aforementioned application can be improved utilizing the method of the current application. In addition, the overcoating of the present invention provides a water proofing that is desirable to reduce the need for special storage and handling conditions prior to use.

The overcoating is a necessary adjunct to the base of photosensitive material for two reasons. First, a water proofing coating is highly desirable to reduce the need forspecial storage and handling conditions, and second, the trace definition of exposed paper is improved considerably by the use of the overcoating. The exact mechanism by which the improved definition is obtained is not known.

The polymer utilized to act as a water proofing agent and a carrier for the other constituents of the overcoating, a' cupric halide and aformate, can be any of a number of commercially available polymers. be an effective water barrier and not affect the sensitivity of the photographic compositions. While other materials prove usable, the most desirable all-around properties have been found with vinyl acetate polymer emulsions.

In order to more particularly set out the features of the present invention, specific examples of preparation technique are presented hereinbelow.

EXAMPLE I In accordance with the preferred embodiment of the resent invention, the followin i O Of course, it must 7 3,105,762 Patented Oct. 1, 1963 Preparation of Silver Nitrate Solution Compound: 7 Amount AgNo 170 gr. (1.0 mol). H O (distilled) 1000 cc. NH (20-30% aqueous solution,

sp. gr. 0.90) 400 cc.

The silver nitrate was weighed and dissolved in the prescribed amount of distilled water. Then the ammonia solution was added with stirring until the solution cleared as the precipitate of silver oxide formed by the first added portions of the ammonia was redissolved.

Potassium Halide Solution Compound: Amount KI 1.66 gr. (0.010 mol). KBr 143 gr. (1.20 mol). H O (distilled) 300 cc.

The potassium iodide was weighted carefully in order to insure precise control over the iodide content of the resultant silver halide mixture. The potassium halides were dissolved in the prescribed amount of water contained in a two-liter beaker which was set in a water-ethylene glycol bath. The bath was heated on a hot plate to about 80 C. The solution of potassium halide was stirred mechanically with a stainless steel stirrer.

Preparation iof Silver Bromo-I odideof its being less soluble than the silver bromide, there may be considerable co-precipitation so that silver iodide is trapped in silver bromide crystals with the result that strained crystals of high sensitivity are formed.

Ammonia and potassium bromide act as solvents for' the silver halides formed and promote crystal growth. Thus, in the presence of these solvents, the smaller silver halide crystals may dissolve and be red-eposited on the surfaces of larger crystals by a process known as Ostwald ripening. This process can occur during the slow precipitation step. The mixture was stirred vigorously with a mechanical stirrer during the precipitation periodf After the precipitation step, the silver halide mixturewas filtered by suction on a. Biichner funnel'and was washed five times with distilled water. It is not normally necessary to dry the silver halides after filteringfand washing.

In addition to the silver bromo-iodide, cadmium iodide was employed to' increase the print-out elfeot and to assist in suppressing background dur'ingla'tensificationf Compound: Amount Silver halide (as prepared hereinabove) ..gr Cadmium iodide ..gr 5' Water (distilled) cc 50 Hydroxyethyl starch (30% hydroxyethyl starch in water solution) gr 67 The ingredients listed above withfthe exception of the hydroxyethyl starch solution were placed in a pint porcelain jar of a ball mill containing 200 grams of one-half inch porcelain pebbles. The bottle was rotated at about 60 rpm. for a period of one hour. The hydroxyethyl starch was then added and the mixture ball-milled for i water.

tor knife to control the thickness of the film. Although the thickness of the coatings to be applied to paper or other supports is dependent on the characteristics desired in the end product, it has been found that if the composition disclosed above is applied in layers calculated to be in the range of about 0.5 mil in thickness a useful product results. As the thickness of the wet film is difficult to measure, it is somewhat easier to use the weight per unit area of solids deposited as a reference. About 1 gram of solids per square foot of the dried film ap pears to be satisfactory. The critical features are that the coating be uniform, flexible, and adherent to the base material. After application to the base plate, the coating was permitted to dry.

Overcoating Mixture Following the above steps we have found that a coating of the following materials provide a surface sensitiZ-ing, Water proofing effect.

Vinyl acetate polymer emulsion gall0ns 1 Distilled water do 1 Cupric chloride solution ml 180 Sodium formate solution ml 3600 Total l gallons 3 The above components are prepared as follows: Vinyl acetate polymer emulsion of approximately 50% solid is used as received. We have found that vinyl acetate polymer emulsion supplied by B. F. Goodrich Chemical Company under their designation Geon Latex (970Xl1) is especially well suited for this purpose.

The cupric chloride solution is prepared by dissolving 25 grams of cupric chloride dihydrate (CuCl .2H O) in 500 ml. of water. Use 60 ml. of this solution for each gallon of overcoating mixture compounded.

The sodium formate solution is prepared by dissolving 40 grams of sodium formate (HCOONa) in 1,600 ml. of Use 1,200 ml. of this solution for each gallon of overcoatin-g mixture to be compounded. The cupric chloride solution and the formate solution are then combined into one solution in the proportion tabulated above, 180 ml. cupric chloride to 3,600 ml. of formate solution.

A blending of the above materials into a common solution must be made in the order in which they are designated above. That is, the vinyl acetate polymer emulsion is first diluted by addition of the distilled water and 'then the cupric chloride solution is added to the mixture of the vinyl acetate polymer emulsion and the dis-tilled water. Unless these steps are followed in the order indi cated there is a possibility of breaking the dispersion oi the vinyl acetate polymer emulsion and water. Blending should be accomplished with sufiicien-t stirring to insure a homogeneous end product- This mixture is applied over the main coating to increase image density and stability. An extremely thin coating suflices. Measurements of coating weight indicate that about 0.3 gram of solid per square foot should be present in the overcoat. This overcoating may be applied in the same manner as noted above. That is,

transfer roller coating, dipcoating using an air-knife to wipe off the excess upon emergence from the bath, or by conventional spreading using a doctor knife to control the thickness of the film. a

EXAMPLE n The pre-treatment of the paper to provide a photosen- 4 sitive coating was the same as in Example I. The

over,-. coating for Example 11 was prepared as follows:

Vinyl acetate polymer emulsion gallons 1 Distilled Water :..Q do 1 OJ-pric bromide solution ml Potassium formate solution ml 3600 Total Q '.gallons 3 The above components are prepared in the same manner as indicated in Example I with the exceptionof the potassium formate solution and cupric bromide solution.

The potassium formate solution is prepared by dissolving 494 grams of potassium formate into 1,600 ml. of H 0.

Use 1,200 ml. of this solution for each gallon of overcoat-- ing mixture to be compounded. The cupric bromide solution is prepared by dissolving 33 grams of cupric bromide into 500 ml. of Water. Use 60 ml. of this solution for each gallon of ovcrcoating mixture. The blend-.

ing of the materials of the overcoating mixture is the same as in Example I. That is, the vinyl acetate polymer emulsion is first diluted by addition of the distilled water and then the mixture of cupric bromide solution and Y potassium formate solution, blended together, are added to the mixture of the vinyl acetate polymer emulsion and distilled water. Th overcoating is applied by any methods of Example 1.

EXAMPLE In The solutions in Example III including the photosensii tive coating initially applied to the paper are prepared in. the same manner as in Example I. The overcoating mix ture is as follows:

Vinyl acetate polymer emulsion gallons "1 Distilled Water; do 1 Cupric chloride solution ml-.. 180 Ammonium formate solution ml-..

Total gallons .3

The above components were prepared in the same manner as indicated in Example I with the exception of theformic acid solution. The ammonium formate solution was prepared by dissolving 350 grams of ammonium formate into 1,600 ml. of water- 'Use of 1,200 ml. of this solution for each gallon of overcoating mixture to be compounded. Again, as in the above examples, the cupric chloride solu- H tion is added to the formate solution to compriseone gallon of the over-all mixture. The blending of the vinyl acetate emulsion, the distilled Water, and the cupric chloride-formate solution follows the same. procedures out lined above. The mixtureis applied in the same manners as'in Examples I and II with a coating thickness equivalent to that previously noted, 0.3 gram of solid per square foot.

The sensitive material and overcoating prepared in ac? cordance with the examples hereinabove was yellow in color, and upon the desired exposure to light, a uniform medium dark brown image or trace having extremely uniform and fine edge definition was'formed. Sensitive. papers, prepared according to this process, were capable of writing speeds equivalent to more than 200,000 inches et al. The Osram lamp is manufactured by Osram, Munich, West Germany and identified as their model of .the 1 composition of the invention produced traces that were much more dense than those traces on identically coated paper Without the 'overcoating. In addition, the traces produced on paper having the overcoating of the invention were more stable than those traces on non-overcoated paper on prolonged exposure to fluorescent light of desk level intensity (50-400 fc.).

Having thus described our invention, What is claimed is:

1. A photosensitive silver halide print-out emulsion having thereon an overcoating consisting essentially of a Water insoluble vinyl acetate polymer emulsion carrier and including as a constituent thereof, cupric halide selected from a class consisting of cupric bromide and cupric chloride, and a compatible Water soluble formate.

2. A photosensitive silver halide print-out emulsion having thereon an overcoating consisting essentially of a Water insoluble vinyl acetate polymer emulsion carrier and including as a constituent thereof cupric chloride and a formate selected from the class consisting of sodium formate, potassium formate, and ammonium form-ate.

3. A photosensitive silver halide print-out emulsion having thereon an overcoating consisting essentially of a Water insoluble vinyl acetate polymeric emulsion carrier and including as a constituent thereof, a cupric halide selected from the class of cupric bromide and cupric chloride, and an alkali metal formate.

4. A photosensitive print-out composition of silver bromoiodide doped with a quantity of cadmium iodide, said composition having thereon an overcoating consisting essentially of a water insoluble vinyl acetate polymeric emulsion carrier having dispersed therein, a cupric halide selected from the class consisting of cupric chloride and cupric bromide, and an alkali metal formate.

No references cited. 

1. A PHOTOSENSITIVE SILVER HALIDE PRINT-OUT EMULSION HAVING THEREON AN OVERCOATING CONSISTING ESSENTIALLY OF A WATER INSOLUBLE VINYL ACETATE POLYMER EMULSION CARRIER AND INCLUDING AS A CONSTITUENT THEREOF, CUPRIC HALIDE SESELECTED FROM A CLASS CONSISTING OF CUPRIC BROMIDE AND CUPRIC CHOLORIDE, AND A COMPATIBLE WATER SOLUBLE FORMATE. 